Paper surface treating devices are well-known in the art, and reference is made to U.S. Pat. No. 3,941,902 for a full disclosure of such apparatus. Typically, a container having a discharge slot or gap applies the treating fluid to a paper web. The discharge slot or gap aperture is usually formed by two spaced parallel guide bars, so that the surface treatment agent flows from the container through the space between the guide bars and on to the paper web, as the paper web is passing over the edges or surfaces of the guide bars. In such arrangements, it is preferable that the paper web be directed away from the gap at an oblique angle relative to an imaginary plane in parallel with the flow direction of the paper web, the oblique angle being illustrated by dotted line 9 in FIG. 1 of the drawings.
It has been found that such arrangements have certain drawbacks. For example, since the discharge slot or gap is formed by two parallel guide bars, the upper surfaces, edges, and corners which are in contact with the paper web are of great importance with respect to the proper functioning of the gap, since the amount of fluid agent to be applied to the paper web depends on the web speed and on controlling the dispensing of the fluid agent from the gap. Therefore, it is important that these surfaces and edges be well defined and not be highly subject to wear. However, this is a difficult problem since the upper surfaces and edges of the guide bars are subjected to a great deal of wear by the paper web. Moreover, the amount of wear or friction can be substantial if the fluid agent being applied includes a pigment, such as may be found in different types of coating agents. Under such circumstances, the edges and surfaces of the guide bars in contact with the paper web are rapidly worn and rounded, which thereby affects the so-called secondary gap, i.e., the space between the paper web and the upper edge of the rearwardly located guide bar. Accordingly, it would be highly desirable to provide an arrangement wherein the paper web moves in a substantially horizontal plane over the guide bars and gap, and in parallel with the upper surface of the guide bars.
Accordingly, it is an object of the present invention to provide an improved arrangement which overcomes the aforesaid problems. Specifically, it is within the contemplation of the present invention to provide a gap arrangement which substantially increases the life of the guide bars, and also allows the pressure applied thereto to be regulated and controlled.